Volkswagen Repair: 92 passat problem w/idle, fuel pumps, engine overhauls

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hi,

I am in western Massachusetts. About three months ago, I had a
problem w/ a fuel pump which caused the motor to overheat some,
not a lot, but it definitley was running on the hot side. since then
the fuel pumps were replaced and it runs fine, except for the revving up. I
just replaced the idle stabilizer valve also ($225). My mechanic
postulates that it could be when it overheated some type of wear on the
valves occured, which is causing the revving somehow. Is this
possible? Have you ever heard of this before? Thank you!

Dan Klimoski
Answer -
Dan, thank you for your question.  The overheating definitely could have caused damage to the
valves, also there could be damage to a sensor that detects RPM of the engine. (I had this happen
on a 4 cyl. Not long ago), which will effect idling.
Hope that helps

Thanks for the info. Is it possible to replace the RPM sensor?

Answer -
Dan, thank you for your folowup question.  The answer is , Yes.  It is possible to replace the rpm
or idle sensor but usually has to have the engine disassembled to do so.  a shop might charge
from $900 to $1800 (my total was around $1500 with parts)  it usually takes around 3 to 8 days
to complete depending upon the availablity of parts.  The sensor is located on or around the
camshaft or the crankshaft (depends on configuration of the engine).  the real cost is in labor,
anywhere from 8 to 20 hours of work.  And only for those VERY experienced to engine overhauls.  
it does not take much to mess up the sensor before installation.
Hope that helps

Don,
I appreciate your help with this. It's a big decision I need to make here. The car has 192K miles
on it. After it warms up and upon coming to a stop, it usually revs up to around 2000 rpms, up
and back down about 8-12 times, then returns to a normal idle. How much longer do you think I
can drive it the way it is? Thank you very much for your advice. Dan Klimoski

Answer
Dan, thank you for your additional question.  With it revving up and down to 2000 numerous times, I really doubt that the problem is even with the RPM sensor.  Sounds more like the idle control sensor or even the EGR valve (probably stuck and needs cleaning or replacing).  Now since this is a 92 (92 models are much harder to find out problems on than say a 96 to 2005 models due to the change in control units), you will not have half the sensors and emission control sensors that are on the newer models.  Another possibility is that the timing belt may need to be replaced (which need replacing about every 65 – 80,000 miles) or there is a vacuum leak near the TBI or carb.  One way to check is once the engine is idling then take a can of WD-40 or carb cleaner, and spray along the vacuum lines (these lines can be black, gray, white or any thing else but are small and usually hard plastic. If the engine revs up, then there's your leak. If it never revs up, then you probably don't have a vacuum leak. Once since you have a 92, you may or may not have an RPM sensor.  They are definitely used on 95 to present, but I am not totally sure about 92's.  As far as drivability, that is a very good question.  It could last for a day, a month, a year before it totally stops running.  But since you have 192k miles on it and I take it that it has never been rebuilt (which is very good!), it might be time to overhaul the engine.  That is something that will happen sometime soon, but when is another question. I usually err on the side of caution (when finances allow) to do an overhaul at the first sign of trouble like severe overheating, valve that could be warped, knocking in the engine, oil leaks or any metal scraping sounds.  
Hope that helps